Electric heater



July 20 1926.

C. P. RANDOLPH ELECTRIC HEATER Filed March 21, 1925 Ivenror Charles l? Randolph,

b9 @my /f His Attorneg.

Patente-d JuIy'zo, 192e.

CHAR-LEB P. RANDOLPH, Ol OAK ILLINOIS,

ABSIGNOB TO EDISON ELEOTBIC APPLIANCE COMPANY, INCORPORATED, OF GHIGAGO, ILLINOIS, A CORPORATION OF NEW YORK.

' morale Hmmm 'Anuman mea umn 21, laas. .semina 17,3415.

My invention relates` to electric heaters and has for its object the provision of a simple and reliable temperature control device for electric heaters.

More specificallyy my invention relates to temperature control means for electriclheating-pads although it obviously has application to various other types of electrically heated devices. Electric heating pads, as commonly constructed, comprise an electric resistance heating unit which is distributed over a comparatively large area. Heat is dissipated by the various portions of the unit substantially independently of each other and consequently there is comparatively little tendency for the exchange of heat and equalization of temperature. 'Phe` "conditions of operation are thus conducive to local overheatilfig;I for example, in case the l dissipation of heat is-obstructed at some point or in the event of a defective heating unit.

In carrying out my invention, I provide a thermostatic control device substantially in the center of the heating pad and provide a plurality of flexible heat conducting members which are arranged to conduct heat from various portions of the pad to the ther- Inostat. In this manner, the thermostat is made responsive to the temperature of the hottest. portion of the pad.

For a more complete understanding of my invention, reference should be had to the accompanying drawing in whichr Fig. 1 is a l Elan view of an electric heating pad, em-

odying my invention; Fig. 2 is a bottom plan view of Fig. 1; Fig. 3 is afragmentary sectional View of Fig. 2 along the line 3--3, looking in the direction of the arrows; Fig.

`^ 4 is a sectional view showing a modified form; while Fig.5 is an enlarged plan view showing the details of the thermostatic control device.

Referring to the drawing, I have shown my invention in one form as applied to an electric heating pad which is provided with a flat spirally wound heating unit 10. This heating unit comprises a central length or rope 11 of suitable fibrous material, such as cotton, on which is wound in helical form a resistance heating conductor 12.` The resistance conductor may be made of any suitable material, such as a nickel-chromium alloy. It is provided with a covering of coti t0n or other fibrous insulating material so that its turns, wound on the central rope 1l, are electrically insulated from each other. Layers of fabric 12 and 12", forming a cover are applied on opposite sides of the dat spiral, 'and the turns of the spiral are secured by sewing the layers of fabric together between the turns as indicated by the line 13.

The first turn at the center of the spiral is made large enough to provide for the insertion of a thermostatic control device or regulator 14 which is included in the electric circuit with the resistance conductor 12. A Aplurality of equally spaced, radially extending, flat, heat conducting strips, 15 to 20 inclu'sive, are provided on one side of the pad. These strips are suitably joined at the center, for example, by making their ends V- shaped and tting them together, as indicated in Fig. 2. The ends of the strips at the center of the pad are also secured to the thermostatic control device in good heat conducting relation therewith. As shown in Fig. 5, the control device is provided with a disc shaped casing 21, the bottom'of which consists of a plurality of radially extending ribs 22 to which the strips 15 to 2O inclusive are secured, for example, by brazing.

Heat is thus conducted by the strips, 15 to 2O inclusive, `directlyto the interior of the casing 21. The strips are made of a material which is flexible and which readily conducts heat, and may be formed of woven or braided strands of copper. They are comparatively thin and bend freely when the pad is rolled, folded etc. In fact, the strlps present no appreciable impediment to bending of the pad. Y

The conducting strips are secured by sew- Y ing them between the fabric layer 12a and an outer fabric layer l2", for example, by sewing the fabric layers together around the strips along the line They may also be placed directly on the turns of the heating unit 10 underneath the cover 12", and secured by sewing through them between the spiral turns of the heatin unit 10, when the two fabric layers 12 an 12b are sewed togetheras indicated in Fig. 4.

As shown in Fig. 5, the thermostatic control device consists of a substantially circular lai-metallic bar thermostat 23 having .on one end an electrically insulated contact 24. The other end of the thermostat is suitably secured, as by riveting, to the inner periphery of the casing 21. Secured also to the casing 21 is a resilient bar 25, made of a single metal, which is substantially the same shape as thermostat 23 but small-er.

The bar 25 carries on its free end an elec` For the purpose of adjusting the contact 26 and thus changing the temperature set-- ting of the device, a cam 29 on which the arm 25 bears is pivotally mounted inthe center of the casing 21. This cam may be turned by means of an arm 30 secured thereto. The end of the arm is bent upward and extends through a slot 31 in the cover 32 ot' the casing 21 so that the contact 26 may be conveniently adjusted from the exterior of the casing. A V-shaped portion 33 of the cover is struck outward somewhat to provide space for the arm 30.

A suitable twin conductorlead 34 terminating in an attachment plug 35 is provided whereby the pad may be connected to the electriccircuit in a well known manner. A snap switch 36 may be provided in the lead 34.

While I have described my invention as embodied in concrete form and as operating in a specific manner in accordance with the provisions of the patentstatutes, it should be understood 'that I do not limit my invention thereto, since various modications thereof will suggest themselves to those skilled in the art Without departing from the spirit of my invention, the scope of which is set forth in the annexed claims.

What I claim as new and desire to secure by Letters Patent of the United States, is

1. Temperature control means for an electrically heated device, comprising temperature responsive means for controlling the heating circuit oit said device, and means for conducting heat to said temperature responsive means from the various portions of said device whereby said control means is responsive to the hottest portion of said device.

2. Temperature control means for an electrically heated device arrangedfor the independent dissipation of heat fromits various portions, comprising a switch forcontrolling the heating circuit of said device, a thermostat for opening and closing said switch, and a plurality of heat conducting members leading from said thermostat to va rious portions of said device whereby said thermostat is responsive to the hottest portion of said device.

3. A temperature control device for electric heating pads comprising a switch in the heating circuit of said pad, a thermostat for controlling said switch, and a plurality ot flexible heat conducting members arranged to conduct heat to said thermostat from the various portions ofsaid pad, whereby said thermostat is responsive to the hottest portion of said pad.

4. A temperature control device for electric heating pads comprising a switch in the heating circuit of said pad, a thermostat for controlling said switch located centrally oi' said pad, and a plurality of iexible, metallic, heat conducting strips leading from said thermostat to the various portions of said pad whereby said thermostat is responsive 'to the hottest portion of said pad.

5. A temperature control device for an electric heating pad comprising a thermostatic control device for the heating circuit of said pad located centrally of said pad, and a plurality of iiexible metallic strips leading radially from said control means to the various portions of said pad whereby said control means is responsive to the hottest portion of said pad.

In witness whereof, I have hereunto set my hand this 17 day of March, 1925.

CHARLES P. RANDOLPH. 

